Check valves are typical of a large number of valve types that employ spring-closed pistons often of polymeric materials which are guided by a surrounding body member. Most present designs employ pistons of generally cylindrical shape. When large tipping displacements occur, many of these pistons jam due to their diagonal dimensions being larger than their guide member's inside diameter. Efforts to reduce jamming have employed small piston diameters, large end chamfered pistons of spherical shaped sides. All of these significantly reduce the end sealing surface. Some piston designs increase the piston to body clearance sufficient to avoid jamming, but this causes reduced piston to seat overlap and loss of sealing insurance. Some designs employ tapered pistons which reduces necessary bearing material for resisting side wear. Such wear results in loss of seat/piston overlap for sealing. As a tapered piston tips slightly, its ability to guide is reduced as its guide-end edges move away from the body guide member. An ideal piston for spring-closed valves would then have maximum front end sealing surface, be contoured to totally eliminate jamming, and provide maximum material along the sides to resist bearing surface wear with its resultant loss of seal surface, but hold guidance constant during tipping motions.
The piston disclosed herein differs from other present inventions in that as the piston tips during normal displacements, the effective guide diameter of the piston remains constant, thereby both eliminating jamming and maintaining constant piston guidance in the body guide member.
The sealing end of the piston is maintained as the largest diameter of the piston, yielding maximum seat/piston overlap to insure effective sealing. Piston side material is maximized to resist bearing wear-caused loss of side material and seal diameter size. The above benefits are accomplished by using a unique semi-toroidal shape for the piston side shape described herein.